Brown's Population Studies and Training Center (PSTC) applies for its fourth round of 5-year Population Research infrastructure funding. The application documents intellectual vitality, trans-disciplinary cooperation and a strong physical and institutional environment for the PSTC. Our application recounts major new investments in faculty and facilities together with the flourishing research activity of continuing program scientists. The PSTC counts 35 faculty among its research associates. Associates have extensive involvement in external research support and are productive scholars. These associates represent three key areas of strength in social science, Anthropology, Economics, and Sociology as well as significant contributions from allied health fields and international studies. This application Program Overview describes the special institutional features that have emerged at the PSTC (Anthropological Demography, African Demography, Primary Data Collection), as well as the signature themes that characterize our substantive research areas (Spatial Population Inquiry, Fertility and HIV/AIDS, Families and Households, Social Behavior and Health, Population and Environment). The application describes the nature of our interdisciplinary cooperation and research, and it presents information about three infrastructure cores (Administrative, Computing and Information Services, and Spatial Analysis) to support that research. It also describes an ambitious Developmental Core with plans to stimulation new interdisciplinary research activity by drawing on significant support from the university and participation from allied health and social science research units at Brown. This application responds to RFA-HD-05-028, Population Research Infrastructure Program.